I need to replace the battery for my 25hp outboard and get a new battery for a MotorGuide 47# thrust 12v trolling motor that I'm getting.

The current boat battery is a deep cycle marine battery. Do I need to replace it with a deep cycle marine battery since the outboard has an alternator?

Is there anything special I have to look for when getting a deep cycle marine battery for a trolling motor?

Thanks

The trolling motor should be hooked up to a deep cycle battery. Even if it his hooked up to an outboard with an alternator. I would get the biggest you can afford and fit in your boat. I have a AC Delco M27MF that has served me well for many years.

A lot of people would recommend using two batteries one for your outboard and one for your trolling motor. The reasoning is a regular starting battery can not handle the deep discharge a trolling motor would give it.  The other is a deep cycle battery can not handle the current a starter can draw from it.

I do not think your 25 HP starter would draw more current that your trolling motor on high.

As mentioned above I have the M27MF battery. I used it for my trolling motor, a 47# 12V Minn Kota, and my 40HP Evinrude electric start. My outboard has a 5 amp charge circuit. I can use the trolling motor all day and still have enough power to start the outboard. I do not rely on the 5 amp charge circuit to keep the battery charged. I always hook the battery up to my 10 amp charger at night and when the boat is not being used.

I can go for a week in Canada on the lake fishing all day running all over and have never been left with a dead battery. I do keep it on the charger when the boat is not in use.